Crimped yarn



Oct. 10, 1967 D. STARKIE ETAL 3,345,815

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CRIMPED YARN Original Filed April 7, 1958 I v 3 Sheets-Sheet 2 Invent r5 Oct. 10,1967 p. STARKIE ETA L CRIMPED YARN Original Filed April '7, 1958 3 Sheets-Sheet 3 United States Patent Ollice 3,345,815 Patented Oct. 10, 1967 3,345,815 CRIMPED YARN David Starkie and Marcus William Astle-Fletcher, Somercotes, England, assignors to English Rose Limited Original application Apr. 7, 1958, Ser. No. 726,928, now Patent No. 3,226,792, dated Jan. 4, 1966. Divided and this application Aug. 29, 1962, Scr. No. 220,331 Claims priority, application Great Britain, Apr. 16, 1957, 12,436/57 2 Claims. (Cl. 57-140) This application is a divisional application of our copending application, Ser. NO. 726,928 filed Apr. 7, 1958, now US. Patent N0. 3,226,792, entitled, Method and Apparatus for Crimping Yarn.

Various types of crimped synthetic fiber yarns are in use in the manufacture of textiles, and particularly of knitted fabrics and garments. The materials from which they are made, such as nylon and other polyamides, Terylene and Orlon, are all thermoplastic materials; that is, when a yarn made from them is held in a folded or crimped form while being subjected to an elevated temperature, it becomes set in that form and retains its crimp at all temperatures below the setting temperature. It will be appreciated that the insertion of crimps in a yarn give it stretc properties. When the yarn is pulled, the crimps unfold and the yarn extends in length; when the pull is removed, the crimps reform and the yarn contracts in length. This crimped form has proved to be of particular value in the construction of fully-fashioned hose. The many desirable properties of a material like nylon for the construction of fully-fashioned hose are well known. By using the same yarn in a crimped form, there are added to these properties the equally desirable characteristics in the hose of close fit and cling during wear, give to the movements of the leg of the wearer, the ability of the hose to fit a range of sizes, and extra warmth and softness to the touch.

One form of crimp which has been used successfully in the manufacture of fully-fashioned hose is a helical construction. In this form the yarn acts as an easily extensible and recoverable spring, and fabrics made from it have these same characteristics of easy extension under pull, together with warmth in wear and softness of handle. One yarn, having this particular construction, is already on the market and is finding wide application in the manufacture of fully-fashioned hose. It is made by drawing a hot yarn, under tension, over an edge, when on subsequently being subjected to a relaxing treatment, the yarn develops a helical crimp. It is important to note that during the drawing over the edge in preparing this particular yarn, one side of the yarn, i.e., that in contact with the edge, becomes flattened, and it will be observed, when the crimp in the yarn has been fully developed, that the flattened side is on the inside of the helix.

The present invention represents an entirely new and improved method of making a stretch yarn of construction similar to the above. The principle, upon which the method is based, has come from observations made during the course of research carried out on the physical properties of thermoplastic fiber-forming materials.

The present invention provides a method of imparting a crimped effect to thermoplastic yarn, which comprises stretching the yarn to cause molecular orientation, heating it, while stretched, in such manner that a temperature gradient is set up across the yarn to heat-set the higher molecular orientation on the side of the yarn exposed to the higher temperature so as to produce a potential crimp owing to the greater capacity of shrinkage at the inside of the helix than at the outside thereof under applied heat, cooling it and permitting it to relax. The

expression cooling it is employed to include permitting 1t to'cool. This method permits the ready production of yarn having stretch properties. The properties of the resultant fabric are enhanced if the yarn, desirably after having been formed into fabric, is submitted While in a relaxed state to further heat treatment at a temperature intermediate the low temperature of the gradient and the highest temperature the fabric is likely to be subjected to. Particularly in the case of stockings this highest temperature is encountered in the pre-boarding operation and may be about 180 C.

The invention further provides a method of imparting a crimped effect to thermoplastic yarn, which consists in stretching the yarn, and rendering permanent the stretch along one side of the yarn by heat treatment.

The invention also provides a method of imparting a substantially helical crimped eifect to thermoplastic yarn, which comprises stretching the yarn, and causing one side of the yarn to retain permanently a greater proportion of the applied stretch by establishing a temperature gradient across the stretched yarn and thereafter cooling and relaxing the yarn.

The invention further provides apparatus for imparting a crimped effect to thermoplastic yarn, comprising means for stretching the yarn, heating means for heating it whilst stretched and for producing a temperature gradient across the yarn, and means for cooling and relaxing the yarn. The invention still further provides a crimped yarn produced by the above method and fabric manufactured from the yarn.

The above and other features of the invention set out in the appended claims are incorporated in the construction which will now be described as a specific embodiment with reference to the accompanying drawings in which:

FIGURE 1 is a section through a filament;

FIGURE 2 is a longitudinal section through a short length of filament treated according to this invention;

FIGURE 3 illustrates the main components of apparatus for carrying out this invention, while,

FIGURE 4 illustrates a length of the crimped yarn in its final form;

FIGURE 5 is a side view of one construction of apparatus according to the invention;

FIGURE 6 is a face view of part of FIGURE 5;

FIGURE 7 is a plan view of FIGURE 6.

Experiments have shown that, if a thermoplastic filament is stretched by a given amount thereby producing a molecular orientation in the filament, and heated to a high temperature while in this state of extension, it will retain all this extension and therewith the corresponding molecular orientation permanently. At lower temperatures, a much smaller amount of extension is retained until a temperature is reached When the filament recovers immediately from the extension. In the case of nylon, the high temperature to cause retention of all the extension must be 210 C. or higher, up to the melting point (250 C.). When the temperature is as low as C., the filament does not retain any permanent extension, recovery being complete once the stretching load has been removed. This fact has been used in devising the new method. Referring to FIGURE 1, the idea is to hold the filament 10 so that it is under strain, and to heat one side of the filament A, but ap-ply no heat to the opposite side B. The heating conditions are selected so that there is formed a suitable temperature gradient across the cross section of the filament from A to B.

Let it be supposed that a nylon 66 monofilament is extended almost to its limit, and surface A is heated to say, 230 0., whereas the temperature of surface B is kept down to about 80 C. On removing the extendin force, surface A will retain its extension of about and therewith its corresponding molecular orientation while surface B will recover from the extension. The filament must, therefore, curl and form a helix with the higher molecular orientation on the outside of the helix. If the filament is then taken and treated in boiling water (the further heat treatment hereinbefore mentioned), the helix will tighten up further. The reason is that the boiling water temperature will cause a further shrinkage on surface B but will have no effect on the heavily heattreated surface A. The total differential shrinkage between the two surfaces A and B, due to these two treatments, will be approximately 20%, and a closely spiralled filament will result. The helix will reverse its spiralled direction every so often in order to avoid overall torsion.

Let it be supposed that the conditions of heating have been selected so that the amount of shrinkage at any point across the filament is proportional to the distance of that point from surface A. FIGURE 2 shows, in diagrammatic form, a section of filament 10 which has been bent into a curve by differential heating and after-treatment in boiling water as described. If the length of the original filament was 100 units, and the outer surface was permanently stabilized under an extension of 10%, it will have a fixed length of 110 units. Upon boiling water treatment, the inner surface would contract a further 10%, say, to give a length of 90 units, i.e., there would be a difference in length between the inner and outer surface of 20 units. The diameter of a denier nylon monofilament is approximately 1.8 thousands of an inch. Let x be the radius of curvature of the section of filament. Then .'.20x=180 and x=9 thousands of an inch. From this, the length of a single spiral, 21rx, =56.5 thousands of an inch.

If such a filament is knitted up to form a fine gauge hose, it has been found that, when the length of one spiral of the filament coincides with that of filament contained in (or constituting) a knitted stitch, the resulting fabric remains virtually uncrimped. It happens that the two, spiral length and stitch length, do approach each other in yarns of this type, and, in consequence, the selection of spiral length and curvature must be chosen very carefully indeed. It has been found that a hose fabric has the best appearance and strength characteristics when the length of the spiral is close to of the stitch length. For fine gauge hose, the stitch length is of the order of '100 thousandths of an inch, and 66 thousandths of an inch would be the ideal length of spiral. As shown by the calculation, the present method applied to a nylon monofilament would allow this, and even a smaller, spiral length to be obtained.

Yarns of denier higher than 15 are composed of a number of 3 denier filaments. Such yarns would be treated, according to our invention, in a virtually untwisted state with the filaments lying side by side to form a flat ri-bbon. The individual 3 denier filaments would be capable of even a shorter crimp length since, for a fixed differential shrinkage, the coil radius and pitch length are proportional to the diameter of the filament.

A number of methods of producing the differential shrinkage of yarns and filaments, constrained in length, are available. Some of these are:

(1) Using heat conduction by contact with a hot surface;

(2) Using differential absorption of radiation, i.e., infrared rays, which is dissipated within the filament in the form of heat;

(3) Treating one side of the yarn with a swelling agent;

(4) By subjecting the yarn to a controlled direction convection draught.

The method which has been used to produce the helical yarn in experimental quantities is method 1. Certain precautions must be taken if the desired effect is to be obtained. If the yarn is heated, at one time, over an appreciable length, it must not be allowed to rotate about its axis, otherwise its whole surface will be heated to the same high temperature. In the case of nylon 66, the hottest temperature must exceed 210 C. if all the extension is to be retained and the smallest size of coil'in the stretch yarn is to be obtained. In instances where larger coil sizes are required, this is governed by the amount of extension and the height of the temperature and conveniently in practice the amount of extension is maintained constant and the temperature is varied according to requirements. For a given temperature at the cool side of the yarn and for a given amount of extension, the size of coil is dependent upon the temperature at the hot side of the yarn. It is preferred to keep the cool side below C. so that in the case of nylon, that side does not retain any permanent extension and to heat the other side to at least C. The yarn must make good contact with the heating surface, and the use of nip rollers may be desirable. If, during heating, the surface of the yarn in contact with the hot surface becomes flattened slightly, there will be a better transference of heat to the yarn. Apart from this, the flattening of the surface has no other significance; it does not correspond to the flattening which takes place during the processing of an existing stretch yarn which has been described earlier. In that case, as already stated, the flattened face is on the inside of the helix; in the crimped yarn made according to the present invention, the flattened face would be on the outside of the helix. In operating the present method successfully, the yarn should preferably be fully extended before the differential heating is applied and not while the heating is being applied in order to obtain the best results. Finally, any sliding over the surfaces used should be avoided in order to prevent rotation of the yarn and obtain the best crimp.

An apparatus for processing the yarn according to the present invention is shown in diagrammatic form in FIG- URE 3. It consists of four positively driven rollers 11, 12, 13 and 14, of which roller 13 is heated. Roller 11 is rotated at a slightly slower peripheral speed than rollers 12, 13, and 14; if the peripheral speed of 11 is S, then those of the other rollers 12, 13 and 14 is 84-10% S. The yarn 10 is wrapped round each of the rollers one or more times. Between rollers 11 and 12, the yarn is extended or drawn 10% in length, and it is taken by the heated roller 13 in that condition. Finally, it is delivered by roller 14 to the usual yarn package. Subsidiary pulleys or guides can be used at each roller to prevent slippage of the yarn. In general, the yarn will be wrapped once only round the heated roller 13, and it may even be wrapped only over a portion of the circumference of that roller. It may be considered advisable to use an auxiliary nip roller in contact with, and rotating at the same speed, as roller 13 in order to ensure a better transfer of heat to the yarn surface. This auxiliary roller might, with advantage, be chilled in order to regulate the temperature gradient across the yarn. The form of the final crimped yarn is indicated in FIGURE 4.

It will be appreciated that by employing the auxiliary nip roller to promote the heat transference the apparatus is capable of processing a helical crimped yarn at high speed. At high speeds it may be necessary to have the temperature of the heated roller in excess of the melting point of the yarn material being processed in order to compensate for the very short time during which the yarn is in contact with the heated surface.

The further heat treatment hereinbefore mentioned can be carried out on the yarn, while the latter is in a relaxed condition, prior to the yarn being knitted into fabric but since this makes the yarn more difficult to deal with, it is preferred to carry out the further treatment on the relaxed fabric itself. The use of boiling water, in which the relaxed fabric is immersed (preferably with agitation), is a convenient way of carrying out the further treatment but heat may be applied in other ways.

The apparatus of FIGURES 5 to 7 can be satisfactorily employed to obtain an economic production of the crimped yarn.

Referring first to FIGURES 5 to 7, there is provided a support structure 15 supporting the rollers 11, 12, 13 and 14 on substantially parallel axes. The yarn 10 travels upwardly from a supply package 16, through conventional tensioning means 17, over stretching rollers 11 and 12 a number of times, partly around a heating roller 13, over drawing-off 0r let-off rollers 14, 18 a numbers of times, and to take ofi means 19.

Drive from a motor 20' is transmitted through a gear unit 21 and chain and sprocket means 22 to the stretching roller 11, the heating roller 13, and drawing-off roller 14. There is also a take-up drive transmission 23 and a clutch control 123. The stretching roller 12 and the roller 13 are idler rollers.

All the rollers 11, 12, 14, and 18 are drum-like and formed with annular grooves 11a, 12a, 14a and 18a for the yarn 10 to travel round them a number of times from one end to the other of the rollers. The stretching rollers 11, 12 step up in diameter from groove to groove so as to be of conical-like form and the drawing-oh rollers 14, 18 are of .parallel form. The idler stretching roller 12 is on an axis slightly inclined (e.g. at 3) to the axis of the driven stretching roller 13, and the idler roller 18 is on on an axis slightly inclined (e.g. at 3) to the axis of the driven roller 14.

The peripheral speed of roller 11 at its smallest diameter is 10% less than, and at its largest diameter is the same as, that of roller 14thereby giving 10 extension to the yarn. By the particular arrangement of the stretching rollers 11, 12 the yarn 10 is extended in a series of small steps up to a point whereat it leaves stretching rollers 11, 12 in a state of the full 10% extension, and the risk of yarn breakage when starting up is at a minimum. The risk of the yarn rolling or twisting, due to the slightly inclined attitude of the yarn coils on both the stretching rollers 11, 12 and. the rollers 14, 1 8, is minimized by the axial inclination of the idler rollers 12, 18 which cause the transfer of the yarn 10 from step to step to take place as nearly as possible in the direction of rotation.

To avoid creep of the yarn 10 in a tendency to reduce the considerable tension on it after it leaves the stretching rollers 11, 12, the driven stretching roller 11 is disposed as close as practicable to the heating roller 13.

The heated roller 13, conveniently of light disc construction, is heated in this example, by disposing round it a block 25 of steel or other metal which is held at the required temperature by any suitable heating means such for example as by two electrical heating elements (not shown) of the resistance type embedded in the block 25, or by other means. Heat losses are reduced by the heated roller 13 being disposed in a close fitting cavity in the block 25 leaving only suflicient of the heated roller 13 exposed for the yarns contact with it, and the outer part of the block 25 is covered with asbestos heat-insulating compound. Mountings for the heated roller 13 are conveniently located outside the block 25 through the medium of an extended spindle and outer bearings, these being consequently kept cool to avoid difficulties of high temperature lubrication. Heat is accurately controlled conveniently by a thermostat in the block 25 and a hand control 113 therefor.

The yarn 10 is pressed into contact with the heated roller 13 'by a smaller diameter auxiliary roller 26 (FIG- UR-E 6') which is of light disc construction and is mounted on a pivoted arm 27 capable of being swung about an axis A parallel to the heated roller axis B. Care is taken to ensure that the axes of the auxiliary roller 26 and of the heated roller 13 are accurately parallel to avoid twisting of the yarn. The two rollers should operate accurately Without wobble. This accuracy is important having regard to the critical dimensions of yarn section and nip between the rollers; for example, when the yarn 10 is a monofilament nylon yarn of 3 denier filament, the nip size is no greater than 0.00076 inch. The auxiliary roller 26 can be chilled for example by directing a flow of cold air on to it say from a pneumatic system which also controls the relation of the auxiliary roller 26 to the heated roller 13. More specifically, the auxiliary roller 26 is biased away from the heated roller 13 by gravity and towards it by a pneumatic piston and cylinder 28 acting on a tail 27a of the pivoted arm 27 (although controllable spring means may be provided for the latter purpose if desired).

There is also provided a yarn deflecting roller 29 which is mounted similarly to the auxiliary roller 26 but spaced therefrom to determine the arc of contact of the yarn 10 with the heated roller 13. The deflecting roller 29 is carried by a pivoted arm 30 capable of being swung about an axis C parallel to the heated roller axis B and gravity biased away from the heated roller 13. A pneumatic piston and cylinder 31 (or controllable spring means) acts on the pivoted arm 31) to bias it towards the heated roller 13.

In the pneumatic arrangement there is also provided (in the pneumatic circuit) an operators on and off valve 32 (FIGURE 7), a key operated needle valve (illustrated at 41 and conveniently disposed remote from the operators valve) and a sensitive gauge (not shown). The turning of an operators on and off handle 33 on a spindle 34 rotate-s a cam 35 which operates the on and off valve 32 and causes a sequence of operations to take place; first, the air pressure line is opened a certain amount; then the deflecting roller 29 is moved to the limit of an adjustable stop 36 (FIGURE 6) to deflect the yarn 10 into contact with a predetermined arc of the heated roller 13 (the stop 36 controlling the final distance of the deflecting roller 29 away from the heated roller 13); and finally the full air pressure is applied against the auxiliary roller 26 to trap the yarn 10 between it and the heated roller 13. The key operated valve 41 is for a supervisor only who alone can operate this (when the operators valve 32 is opened) to control the air pressure applied to the auxiliary roller 26.

There is further provided a pair of eccentrics 37, 38 on the spindle 34 cooperating with the tail 27a and a tail 30a of the pivoted arms 27, 30 respectively for adjustably displacing the two rollers 26, 29 away from the heated roller 13 when the valve 32 is off thereby allowing for threading up of the yarn 10. When the valve 32 is on there is a gap between the tail 27a and the eccentric 37 to allow necessary resilience of the auxiliary roller 26 under the applied air pressure.

There may also be a start and stop switch 39 and an operating cam 40 therefor on the spindle 34.

In threading up, a length of yarn 10 is pulled from the supply package and its free end is attached to the take-oif means; the pulled-oft" yarn is then wrapped round the grooves of the rollers 14, 18 in the correct sequence; the yarn is then passed through the spaces between the separated heated roller, auxiliary roller and deflecting roller, and next it is passed around the grooves in the stretching rollers 11, 12 in the correct sequence; finally the yarn is passed through the tensioning device adjacent the supply package.

It will be appreciated that in operation of the apparatus, the yarn is stretched to the appropriate extent by rollers 11, 12, and while in the stretched condition has one side heated and is received by rollers 14, 18. These rollers 14, 18 maintain the yarn substantially in its stretch-ed condition while it cools. When the yarn is sur- "7 rendered by rollers 14, 18, it relaxes and cools (or may cool) further. In the relaxed and cooled yarn, that side thereof which Was heated retains at least some of the applied extension and so the yarn assumes a helical form.

We claim:

1. A crimped thermoplastic yarn, comprising a plurality of crimped, continuous, thermoplastic filaments, each of Which is of generally helical configuration, has a higher molecular orientation at the outside of the helix than at the inside thereof, and under applied heat, exhibits a greater capacity for shrinkage at the inside of the helix than at the outside thereof.

2. A crimped thermoplastic yarn according to claim 1, wherein the outside of the helix has a flattened configuration.

8 References Cited UNITED STATES PATENTS 2,919,534 1/1960 Bolinger et al 28-72 2,974,391 3/ 1961 Spealeman et al 281 3,028,653 4/1962 Evans 2872 FOREIGN PATENTS 206,681 2/ 1957 Australia. 522,045 2/ 1954 Belgium. 558,297 12/ 1943 Great Britain.

564,382 10/1958 Canada.

FRANK J. COHEN, Primary Examiner.

R. MADER, Examiner.

J. PETRAKES, H. G. GARNER, Assistant Examiners. 

1. A CRIMPED THERMOPLASTIC YARN, COMPRISING A PLURALITY OF CRIMPED, CONTINUOUS, THERMOPLASTIC FILAMENTS EACH OF WHICH IS OF GENERALLY HELICAL CONFIGURATION, HAS A HIGHER MOLECULAR ORIENTATION AT THE OUTSIDE OF THE HELIX THAN AT THE INSIDE THEREOF, AND UNDER APPLIED HEAT, EXHIBITS A GREATER CAPACITY FOR SHRINKAGE AT THE INSIDE OF THE HELIX THAN AT THE OUTSIDE THEREOF.
 2. A CRIMPED THERMOPLASTIC YARN ACCORDING TO CLAIM 1, WHEREIN THE OUTSIDE OF THE HELIX HAS A FLATTENED CONFIGURATION. 